MongoDB calculate count on date grouping - mongodb

Question

I want to calculate the allotment count of each day, by using day grouping on assigned_on I am able to get assignment count of each day, but those are unique count of each day.
In that count I also want that bed to be included which was assigned yesterday or few days before but not yet released.
For example, I have following records
{
"assigned_on":ISODate("2015-12-01T00:00:00Z"),
"released_on":ISODate("2015-12-01T14:01:23Z"),
"bed_id":1
},
{
"assigned_on":ISODate("2015-12-01T00:00:00Z"),
"released_on":ISODate("2015-12-04T14:01:23Z"),
"bed_id":2
},
{
"assigned_on":ISODate("2015-12-01T00:00:00Z"),
"released_on":ISODate("2015-12-01T14:01:23Z"),
"bed_id":3
},
{
"assigned_on":ISODate("2015-12-02T00:00:00Z"),
"released_on":ISODate("2015-12-02T14:01:23Z"),
"bed_id":1
},
{
"assigned_on":ISODate("2015-12-02T00:00:00Z"),
"released_on":ISODate("2015-12-02T14:01:23Z"),
"bed_id":3
},
{
"assigned_on":ISODate("2015-12-03T00:00:00Z"),
"released_on":ISODate("2015-12-03T14:01:23Z"),
"bed_id":1
},
{
"assigned_on":ISODate("2015-12-03T00:00:00Z"),
"released_on":ISODate("2015-12-03T14:01:23Z"),
"bed_id":3
}
Current query
db.test.aggregate([
{
"$match": {
"assigned_on": {
"$gte": ISODate("2015-12-01T00:00:00Z"),
"$lt": ISODate("2015-12-03T23:59:59Z")
}
}
},
{
"$group": {
"_id": {
"$dayOfMonth": "$assigned_on"
},
"Count": {
"$sum": 1
}
}
}
])
As by day grouping on assigned_on I get above result for day 1, 2 and 3, but I want to the Count for day 1, 2 and 3 as 3 for each in result because in second record the released_on date is 4th december which means that bed 2 was occupied on day 1, 2, 3 and 4.
Current output :
{ "_id" : 3, "Count" : 2 }
{ "_id" : 2, "Count" : 2 }
{ "_id" : 1, "Count" : 3 }
Expected output :
{ "_id" : 3, "Count" : 3 }
{ "_id" : 2, "Count" : 3 }
{ "_id" : 1, "Count" : 3 }
Edit : The _id are the dates that is 1st December, 2nd December and 3rd December and count are the number of beds allotted on respective days
An help or pointer will be very helpful

Answer 1

You can do it with the mongodb mapReduce:
var map = function(){
var startDate = new Date(this.assigned_on.getTime());
//set time to midnight
startDate.setHours(0,0,0,0);
//foreach date in date range [assigned_on, released_on) emit date with value(count) 1
for (var date = startDate; date < this.released_on; date.setDate(date.getDate() + 1)) {
if(this.bed_id) {
emit(date, 1);
}
}
};
//calculate total count foreach emitted date(key)
var reduce = function(key, values){
return Array.sum(values)
};
db.collection.mapReduce(map, reduce, {out : {inline : 1}}, callback);
For your data I got such result:
[ { _id: Tue Dec 01 2015 02:00:00 GMT+0200 (EET), value: 3 },
{ _id: Wed Dec 02 2015 02:00:00 GMT+0200 (EET), value: 3 },
{ _id: Thu Dec 03 2015 02:00:00 GMT+0200 (EET), value: 3 },
{ _id: Fri Dec 04 2015 02:00:00 GMT+0200 (EET), value: 1 } ]